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From: John Baldwin <jhb@freebsd.org>
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Date: Wed, 21 Oct 2009 13:49:09 -0400
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Cc: Alexander Best <alexbestms@math.uni-muenster.de>
Subject: Re: mmap(2) with MAP_ANON honouring offset although it shouldn't
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On Wednesday 21 October 2009 11:51:04 am Alexander Best wrote:
> although the mmap(2) manual states in section MAP_ANON:
> 
> "The offset argument is ignored."
> 
> this doesn't seem to be true. running
> 
> printf("%p\n", mmap((void*)0x1000, 0x1000, PROT_NONE, MAP_ANON, -1,
> 0x12345678));
> 
> and
> 
> printf("%p\n", mmap((void*)0x1000, 0x1000, PROT_NONE, MAP_ANON, -1, 0));
> 
> produces different outputs. i've attached a patch to solve the problem. the
> patch is similar to the one proposed in this PR, but should apply cleanly to
> CURRENT: http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/71258

A simpler patch would be to simply set pos = 0 below the MAP_STACK line if 
MAP_ANON is set.

-- 
John Baldwin